Pollen allergy / hay fever is caused by plant pollen. The symptoms include sneezing, running nose, stuffy nose, and itchy eyes. Japanese cedar pollinosis is the most common among all and its pollen maximizes between late February and the end of April. Other common causative plants include alder, cypress, anthoxanthum odoratum, orchard grass, and timothy, and their maximum season differs depending on the kind of plants.

The management includes oral antihistamines, eye drops, and nasal drops. For Japanese cedar pollinosis, sublingual immunotherapy is available. This has to be started only after the definitive diagnosis with blood test or other methods. It can be started during the time of the year except the maximum pollen periods between February and May. After the start of this treatment, patients are required to come back in 2 weeks, and then bimonthly consult is necessary.